Some liquids must be completely debubbled prior to use. For example, blood should be almost completely debubbled prior to its introduction into a patient, since it has been found that patients who are transfused for long periods of time with biological fluids are subject to confusion and disorientation. Further, in some instances, necrosis of brain and lung tissue has been found to occur. It is believed that these problems arise due to blockage of small blood vessels by microscopic gas bubbles introduced with the fluid supply.
Filters of polymeric material have long been used to remove bubbles from biological fluids, including blood supplies; such filters, however, are often inefficient. Further, these filters are incapable of reliably eliminating gas bubbles below a certain size.
Various devices have been developed that degassify liquids through the use of sound waves. Most of these devices isotropically agitate gas bubbles in a manner which makes them combine and buoyantly rise to a vapor-liquid interface, or surface. These types of device therefore, favor bubble growth and speeds up the normal outgassing of liquids streams. An example of such a device can be found in U.S. Pat. No. 3,904,392 to Van Ingen et al, in which a resonant ultrasonic horn is used to agitate bubbles which then rise to a depressurized vapor-liquid interface.
An alternate approach is to use sound waves to break up existing bubbles in a liquid and cause them to dissolve. Such devices thereby change the gas solubility of the liquid to remove the bubbles. A device using this approach is described in U.S. Pat. No. 4,205,966 to Horikawa.
Existing sonic devices, as described above, constitute an advance in the art but suffer a critical disadvantage, among others, that is particularly significant in relation to biological fluids such as blood. All these devices harmfully affect blood chemistry. The violent agitation of a liquid, as called for by some of these devices, would, in blood, result in the destruction of living blood cells, or hemolysis, due to fluid cavitation and cell rupture. Further, modification of the gas solubility of blood, as performed in others of these devices, can also have harmful effects on the blood cells. Additionally, it may permit later reformation of damaging gas bubbles.
It is an object of this invention, therefore, to provide a sonic debubbling device capable of physically removing bubbles from a liquid, particularly a biological liquid, in a non-destructive manner which leaves the liquid's gas solubility substantially unchanged.